1. Field of Invention
The present invention relates to a method and apparatus of pointing stick device, and more particularly to a method and apparatus of pointing stick device using in compact electronics devices with reduced cost.
2. Description of Related Arts
A pointing stick device is first used in laptop computer for controlling the movement and position of the cursor. Most of pointing stick devices is also known as isometric joysticks because they are operated by sensing applied forces through two or more pairs of resistive strain gauges. Generally a pointing stick device includes a cantilever, and two pairs of strain gauges coupled with the cantilever. When the cantilever is exerted with force and generates deformation, the strain gauges will sense it and generate electronic signal. Then this signal can be used to control other devices such as a cursor.
The advantage of a pointing stick device is it can be operated by one finger, and this finger doesn't need to be moved away from the pointing stick. But in order to sense the force exerted by the finger which is normally very weak, the pointing stick device needs to be very sensitive. For this reason, the tolerance of the components is very low. For example, the current available products highly depend on accurate voltage sources cooperating with resistors as power resource and reference voltage. The current source is conveniently provided by many integrated chips such as micro controller unit (MCU), and is programmable. Doesn't like current source, voltage source needs extra separate to provide particular voltage level, and the voltage level is not adjustable. The precision is anther important issue. For acceptable performance, the precision of the sensors (strain gauges) is requested to be less than 2˜3% which is expensive. This increases the cost, part count, and device space.
Device space is always highly considered in compact electronic equipment. The more external components are used, the more space is taken. Current products are using more than 30 external components which have a large edge to reduce. Another issue of compact electronic equipment is radio frequency noise. As the dimension of the circuit is getting smaller and smaller, electric magnetic interference, such as cell phone signal, is much easier to be introduced. The effect is magnificent especially for sensitive devices. The common solution is using different kinds of filters. But it is obvious that using filters will increase the cost, and make the system more complex. Besides these considerations, there is always an attempt for the device to perform faster and more accurate. Therefore, both the circuit and the operation process are necessary to be improved for a better performance.